The present invention relates to a bicycle tire which is made foldable by embedding in the bead sections, bead cores of thin strands of hardened steel or twisted cords which are made of light and flexible non-organic or organic fibrous material.
Heretofore, ring-shaped bead wires have been employed for the bead section of a bicycle tire. Such a bead wire has a high rigidity and repulsive elasticity and therefore it will stretch very little so that a tire using such bead wires can be firmly fitted onto a rim. Furthermore, the bead wire is sufficiently strong to function as a bead core. However, since the bead wire has a low flexibility, the bead wire cannot be folded. Accordingly, the bead wires must be stored or shipped as they are, that is, it is impossible to deform them for storage or shipping. Thus, the conventional bead wire suffers from a drawback in that it is impossible to closely pack them.
A tire of this type includes, in general, the following three essential members:
(1) An unvulcanized tread rubber member which is formed by extruding kneaded compound rubber into a trapezoidal form, or with the use of a calender, in such a manner that the central or the tread portion thereof is thick while the side portions are thin.
(2) A carcass member made of a belt-shaped tire fabric which is formed according to a method in which an organic or non-organic fibrous cord fabric woven in the form of a tire fabric is subjected to adhesion treatment, covered with rubber cement and subjected to friction treatment or rubber coating, and the fibrous cord fabric thus treated is cut on the bias (usually at 15.degree. to 70.degree.) into pieces of tire fabric which are joined together to form a belt-shaped tire fabric.
(3) An endless bead wire which is fabricated according to a method in which a hardened steel wire covered with rubber is wound in the form of a coil a plurality of turns according to the dimensions of a tire to be manufactured, or a piece of hardened steel wire is annularly formed and both ends thereof are welded together or connected together with a nipple into an endless hardened steel wire.
The following methods have been employed for manufacturing the above-described tire:
(1) A carcass tire fabric having a predetermined width and length is wound endlessly on a separable drum having two bead wire grooves in its outer wall spaced a predetermined distance from each other, or on a stretchable forming drum having a plurality of segments by deforming a portion of the drum, or by reducing the circumferential length of the drum, i.e. contracting the drum. Then, two ring-shaped or coil-shaped bead wires, which are fabricated in a separate manufacturing step, are positioned on the carcass tire fabric manually or by another suitable method. Thereafter, the bead wires are tensioned on the drum by restoring the deformed drum or expanding the contracted segments of the drum. Then, both sides of the carcass are folded inwardly along the bead wires manually or by using a conventional folding device so that they overlap in the central portion of the carcass. Thereafter, the two sides are depressed with a roller or the like to form plies of the carcass. An unvulcanized tread rubber member which is fabricated in a separate manufacturing process is bonded to the plies or the carcass under pressure to form the tire.
(2) Two plies of carcass tire fabrics having opposite bias angle directions are wound on the outer wall of the drum employed in the above-described method (1). More specifically, a carcass tire fabric woven in one bias angle direction and having a width slightly larger than the distance between the bead grooves is wound, as the first ply of carcass tire fabric, on the drum, and a carcass tire fabric woven in the opposite bias angle direction and having a width slightly smaller than that of the first ply of carcass tire fabric is wound thereon in such a manner that, when the two plys of carcass tire fabric are folded, the edges thereof are spaced apart from each other at each side (see FIGS. 8 and 9). Similarly as in the above-described method (1), a pair of bead wires are placed on the two plys of carcass tire fabric along the bead grooves, both ends of the two plys of carcass tire are folded, and a tread rubber member is bonded thereto.
(3) In a third method, a two-drum system is employed using two drums on each of which are formed two bead wire grooves spaced a predetermined distance apart from each other. One pair of bead wires is set in the bead grooves of the two drums and are tensioned by increaseing the distance between the axes of the two drums with an air cylinder. (In the two-drum system, the distance between the axes of the drums can be adjusted with an air cylinder or the like). Tire fabrics, each having a predetermined width in the direction of arrangement of tire fabric cords, wound on two spools are laid over the bead wires by spirally winding the two spools around the two bead wires while simultaneously turning the drums to move the bead wires. Then, the tire fabrics are depressed against the drum with a roller to form a tire carcass and an unvulcanized rubber member is bonded to the tire carcass to form the tire.
In each of the above-described conventional methods, the essential members, namely, the tread rubber member, the carcass tire fabric and the bead wire which have been fabricated in separate manufacturing processes, are employed. Of these essential members, the bead wires serving as the tensile members of a tire are especially flexible making it difficult to maintain them circular. This restrains the automatic formation of tires.
Tires formed according to the above-described methods are unsatisfactory in quality. If the size and specification of a tire is changed, it is necessary to change the specification and dimension of the bead wire used. It is necessary to have on hand a variety of forming drums as it is also necessary to use different forming drums for bead wires of different dimensions. This is uneconomical. Furthermore, whenever the tire size is changed, the forming drum must be changed. Thus, the conventional methods are disadvantageous in the number of manufacturing steps, in the time required to manufacture the tires and in safety.
In general, the bead wires fabricated in the separate manufacturing process are bundled at a density of 100 to 500 pieces/bundle for storage. For this purpose, an adhesion preventing agent is applied to the bead wires so that, during storage or transport, they do not adhere to one another through the rubber covering thereof. The adhesion preventing agent later adversely affects the bonding of the bead wires to the carcass during the manufacturing process. Furthermore, during transport, the rubber covering the bead wires tends to deform due to the adhesion preventing agent. Accordingly, a tire having a correct configuration and dimensions cannot be produced. Also, as described above, since a number or bead wires are bundled for storage and tend to cling to one another, prior to manufacture of tires, it is necessary to manually separate the bead wires from one another, which is time consuming. In addition, the bead wires may be deformed to the extent that they cannot be used.